Best way to determine user's screensize?

[flaskee]

Perhaps a more tactical approach would best to figure
out how to do cross-platform python apps.

What is the best approach to determining the user's available screensize,
when they open your python application?

Note that the "desktop" application could be running on Android, iOS,
MacOS, Windows or Linux (I think that I understand how to handle it for browser-based things.)

As close to an all Python answer as possible, would be optimal.

Thank you!